Computer Network Assignment A134613
'INTRODUCTION' A computer network may be defined as the coordination or interconnection of a number of individual computers. A computer network is basically established by the network layer in the Open Systems Infrastructure model, popularly known as the OSI model. A computer network is a collection of computers or digital devices ("nodes") connected by telecummunication links or other networks. The network allows the computers to share resourses workloads, or data. The communications on the network follow aprocol that determines how data is encoded, how access to thr network is handled, and how errors are reported and corrected. These rules of communication are understood by all participants. 'BACKGROUND' Network Access Control (NAC) is a computer networking solution that uses a set of protocols to define and implement a policy that describes how to secure access to network nodes by devices when they initially attempt to access the network. NAC might integrate the automatic remediation process (fixing non-compliant nodes before allowing access) into the network systems, allowing the network infrastructure such as routers, switches and firewalls to work together with back office servers and end user computing equipment to ensure the information system is operating securely before interoperability is allowed. 'BENEFITS' There are several benefits of computer network *''Facilitating communications - Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing. *Sharing hardware - In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer. *Sharing files, data, and information - In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks. *Sharing software - Users connected to a network may run application programs on remote computers. 'WHAT IS NETWORK CLASSIFICATIONS' Computer networks can be classified by means of a lot of types like the network size, structure, mode of connectivity, topology and others. Some of them are, '''Network Size' Considering the size of the implemented network, Computer networks are classified into 3 main divisions namely Local Area Network (LAN), Wide Area Network (WAN) and Metropolitan Area Network (MAN). In certain fields, they are also further classified into Personal Area Network (PAN), Campus Area Network (CAN) and Global Area Network (GAN). *'LAN: -' A network of computers which cover only a small area like an office or a building can be referred to as a Local Area Network. All the individual computers must have a common protocol layer for their connectivity with the basic functionality taking place at the network layer. In general, LANs are based on Ethernet technology. *'WAN: -' Wide Area Network is basically an extension of the Local Area Network except for the fact that the size of the network extends to a very large area. The major functionality of the WAN networks take place at the 3 lower layers of the OSI model namely network layer, data link layer and the physical layer. *'MAN: -' Metropolitan Area network is a combination of two or more individual Local Area Networks but with a small criterion of the boundary of the network not exceeding the city limits, thus integrating the network as a single unit within a city. *'PAN: -' Personal network is the smallest of all networks with most of the networks not exceeding a total size of 25 feet. *'CAN: -' This is similar to a wide area network but the size of the network is limited to a certain social limit, for example the network in an university where the total network is formed by the collaboration of more than one Local Area Network. *'GAN: -' Global Area Networks are large scale WANs and are implemented globally. The total network consists of a large number of sub-networks with most of the connectivity between the networks is done using wireless networks. Structure Of The Network Considering the structure and relationship between the elements of a computer network, the network may be classified into 3 divisions namely Client-Server model, Peer to Peer model and Active Networking model. Each of the classifications has a separate and unique structure which differentiates them in connectivity and working mode. Mode of Connectivity By means of the connection mechanisms, computer networks are divided into wired networks and wireless networks. The wired networks are further divided into some sub-divisions like Optical Fiber and Ethernet networks. Topology In general, a computer network is technically classified based on the topology of the total network which includes the structure of the networks too. They are divided into Bus networks, Ring network, Star network, Mesh network, Star-bus network, Tree network. Hardware Requirements for a Network Set-Up Other than the computers required for a network establishment, the requirement arises for other hardware components too. Some of them are, Routers Routers simply function as an intermediary device which forwards the data packets that it receives, to the next available or neighboring router or a terminal. Switches Switches are the virtual controllers of routers and bridges. These are operated from each of the individual layers of the OSI layer. Certain cases where the devices operate on multiple layers are called multilayer switch. Bridges Technically, a bridge acts a connector between the data link layer and the network layer. The three types of bridges are Local Bridges, Remote Bridges and Wireless bridges. Network Cards Network cards are the most important hardware component of a computer network. The most important functionality of the layer is to enable communication between the computers in a network. 'TWO TYPES OF NETWORKS BASED ON PHYSICAL SCOPE' Wide area network A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model, the physical layer, the data link layer, and the network layer. Campus network A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area. The networking equipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.). In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls. 'BASIC HARDWARE COMPONENTS' All networks are made up of basic hardware building blocks to interconnect network nodes such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cabel). Less common are microwave links or optical cable ("optical fiber"). Network interface cards A network card network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. Repeaters A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. Repeaters work on the Physical Layer of the OSI model. Hubs A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address.It works on the Physical Layer of the OSI model. Bridges A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges broadcast to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address to that port only. Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived. Bridges come in three basic types: *Local bridges: Directly connect local area networks (LANs) *Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers. *Wireless bridges: Can be used to join LANs or connect remote stations to LANs. Switches A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches. Some switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The term switch is used loosely in marketing to encompass devices including routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Routers A routers is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data). 'CONCLUSION' A network may require one engineer to design it, another engineer to build it, and another engineer entirely to administer it. The skills needed for each stage in the process are related but not necessarily dependent; hence, Networking is interdisciplinary. The distinction between Networking and Computer Science in general is difficult to precisely define; it is better perhaps to consider that Networking grew out of Computer Science, because of a need to extend the existing capabilities of a computer (which includes data transmission) across large distances and with other unlike systems. However, an extensive background in Computer Science is not necessary to study or even practice Networking. A Network Engineer is a qualified individual who works with networks of some form, but the scope of that work and the skills required may be as diverse - even from one job to the next - as those of any scientist 'REFERENCES' *http://en.wikipedia.org/wiki/Computer_network *http://en.citizendium.org/wiki/Computer_network *http://www.buzzle.com/articles/computer-network.html *